Washing household appliances such as dishwashers and/or washing machines comprise a water circulation pump unit to recirculate the water during the washing processes, and a drainage pump unit to drain water during a drainage process, which normally rotates at a specific speed of rotation and for a specific time.
Drainage pump units comprise an impeller and, generally, a permanent-magnet synchronous motor to allow the impeller to rotate at a determined speed of rotation and thereby drain the water, as is the case, for example, of those disclosed in patent documents EP 287984 B1 and ES 2162544 B1. Synchronous motors are connected to the mains supply, and comprise a determined network frequency, the speed of rotation of the impeller depending on the network frequency which is normally substantially constant. The drainage flow depends on the speed of rotation of the impeller and therefore on the frequency applied to the synchronous motor.
Washing household appliances can also comprise control means for controlling the supply to the drainage pump unit, which allow the units to activate at a specific time and which deactivate following a specific time interval, when the programme cycle has finished or when it is deemed convenient. This may be set beforehand depending on the washing program to be used, for example, and the control means have the function of activating the pump unit to begin the drainage process during which the drainage pump unit allows the drainage of the water, and of deactivating the unit to finish the drainage process. As a result, the drainage processes require that the drainage pump unit is active for a preset time at the preset frequency, without taking into consideration parameters that may optimise or improve the efficiency of the processes or which may even improve the reliability of the drainage pump units. This may result in a premature fault in the drainage pump unit, and due to the tendency to concentrate components in washing appliances it may become increasingly difficult to replace the unit.
There are known washing household appliances that overcome this drawback by providing the pump unit with more generous dimensions that increase pump capacity and decrease activation time of the pump. A problem with this solution is that it results in increased manufacturing costs and adversely affects the ability to scale the dimensions of the appliance in which the drain pump is incorporated. Some washing household appliances comprise control means to resolve these drawbacks, thereby avoiding the need for a provision of more generous dimensions, the control means being adapted to control the supply to the drainage pump unit not only to start and end the drainage process, but also to control the supply during the drainage process.
Document EP1942219A1, for example, discloses a washing household appliance of this type. The control means comprised in the appliance may allow the drainage pump unit to activate and/or deactivate during the drainage process. The household appliance thus comprises level sensors to detect the level of the water, and the control means may determine the level in accordance with the detection of the level sensor. The control means thus allow, during the drainage process, the drainage pump unit to activate at a specific frequency or to deactivate the pump unit, in accordance with the detected level, thereby creating a more effective process and also increasing the reliability of the drainage pump unit as it is active for less time in each drainage process.
In some washing household appliances a variable-frequency drainage pump unit is used and which comprises an impeller and a BLDC type motor to allow the rotation of the impeller. Document EP1783264A2, for example, discloses an appliance that comprises a motor of this type, and also discloses a control method for improving control over the drainage pump unit. The consumption current of the motor is determined, and the current is linked to a water level. The frequency of the motor supply voltage is changed to vary the flow of drainage water in accordance with the associated water level. As a result, the control means also compare the associated level with a preset level.